Anisotropic magnetization and electronic structure of the first-order ferrimagnet ErCo₂ studied by polarization dependent hard X-ray photoemission spectroscopy

The first-order ferrimagnet ErCo₂ attracts interest not only because of metamagnetism and magnetocaloric effect just above T_C ≈ 32–34 K but also because it is closely related with the itinerant metamagnetism of YCo₂ and LuCo₂. We study the electronic structure of single crystals with hard X-ray photoemission spectroscopy (HAXPES). Magnetization measurements reconfirm the first-order magnetic transition, metamagnetism, and strong magnetic anisotropy. Calculated ErCo₂ band structures of the ferrimagnetic and paramagnetic phases are presented in detail. In the ferrimagnetic state, the density of states just below E_F is smaller than in the paramagnetic phase. Valence band spectra in the paramagnetic state show strong polarization dependence. Furthermore, the change across the first-order ferrimagnetic transition in the valence band electronic structures is observed. These experimental data are well described by the band structure calculation incorporated with the polarization dependent cross-sections of orbitals. We further discuss possible effects of electron correlation and spin fluctuation.